Process for producing steel sheets for cans high in the anticorrosion

ABSTRACT

A PROCESS FOR PRODUCING STEEL SHEETS FOR CANS WHICH ARE HIGH IN THE WORKABILTIY, PARTICULARLY IN THE CAN-PRODUCING PROPERTY AND IN THE ANTICORROSION, PARTICULARLY ADAPTED TO STORE CARABONATED BEVERAGES, COMPRISING HOT-ROLLING AN EXTREMEMLY LOW CARBON STEEL MATERIAL CONTAINING LESS THAN 0.030% C, AND 0.02-0.10% S AND OF S/P&gt;1 AND THEN COLD-ROLLING THE THUS OBTAINED HOT-ROLLED STEEL SHEET IN ONE STEP AT HIGH REDUCTION RATE TO A PRODUCT OF FINAL GAUGE OF LESS THAN 0.5 MM.

0d. 26, 19' TQSHIRQ N|SH|HARA EI'AL 3,614,886

PROCESS FOR PRODUCING STEEL SHEETS FOR CANS HIGH IN THE ANTICORROSION Filed Jan. 26, 1970 2 Sheets-Sheet l Relolion b elween [C] Conlenl of As-Cold Rolled Sleel and Blue Dye Value [s] unoddetL O 0.02 O04 O06 INVENTOR Toshiro Nishihara Hidejiro Asano Yashichi Ouyagi B umw (PM ATTORNEB Effervescem beverage conlife (months) PROCESS FOR PRODUCING STEEL SHEETS FOR CANS Filed Jan. 26, 1970 HIGH IN THE ANTICORROSION 2 Shects-Shuet [3 Cold-reducfion rate of 30% reduction rate of 50% Cold-reduction rate of 90% W 3;. I ATTORNEYS United States Patent O 3,614,886 PROCESS FOR PRODUCING STEEL SHEETS FOR CANS HIGH IN THE ANTICORROSION Toshiro Nishihara, Hidejiro Asano, and Yashichi Ouyagi,

Kitakyushu, Japan, assignors to Nippon Steel Corporation, Tokyo, Japan Filed Jan. 26, 1970, Ser. No. 5,495 Claims priority, application Japan, Feb. 3, 1969, 44/ 8,059 Int. Cl. B21b 3/02 US. Cl. 72365 4 Claims ABSTRACT OF THE DISCLOSURE A process for producing steel sheets for cans which are high in the workability, particularly in the can-producing property and in the anticorrosion, particularly adapted to store carbonated beverages, comprising hot-rolling an extremely low carbon steel material containing less than 0.030% C, and 0.020.10% S and of S/P 1 and then cold-rolling the thus obtained hot-rolled steel sheet in one step at high reduction rate to a product of final gauge of less than 0.5 mm.

BACKGROUND OF THE INVENTION 'Field of the invention This invention relates to steel sheets for cans which are high in the anticorrosion, are particularly adapted to store substances (which shall be called carbonated beverages), which generate or contain carbon dioxide strong in the corrosion, and are high in the workability and particularly in the can-making property. More particularly, the present invention is to obtain a steel sheet for cans of a thickness of 0.5 mm. and hardness of T-6 by coldrolling in one step at a high reduction rate a hot-rolled steel sheet containing less than 0.03% C or preferably less than 0.018% C and 0.020.10% S and of S/P l.

Description of the prior art Generally, even if a conventional tin-plated or galvanized steel sheet is used as a steel sheet for cans to contain so-called carbonated beverages as substances, which generate or contain carbon dioxide, the tin does not exhibit a sulficient anticorroding action on the steel sheet. Therefore, the steel sheet itself has come to be required to have a strong anticorrosion against the contents.

As developed from such viewpoint, there is disclosed a steel sheet in the specification of US. Pat. 3,392,014.

In said specification are mentioned a steel sheet for cans to contain phosphoric acid series carbonated beverages, Which sheet contains 0.02-0.20% C and 0.02- 0.10% S and is of S/P 1, and a steel sheet for cans to contain carbonated beverages containing an organic acid mainly composed of critic acid and a phosphoric acid series, which steel contains 0.10.3% Cu.

As a result of further investigating the corrosion mechanism of the above-mentioned steel sheet with carbonated beverages, the inventors of the present invention have discovered that C is an important factor with respect to S. At the same time, as a result of investigating a method of obtaining cheap steel sheets, they have discovered that a 3,614,886 Patented Oct. 26, 1971 steel sheet having a high anticorrosion and wonkability can be produced by properly reducing the C content even with a full hard material prepared by strong cold-rolling in one step.

SUMMARY OF THE INVENTION Therefore, the present invention has for a main object to provide a steel sheet high in the anticorrosion particularly against carbonated beverages and the work-ability by extremely reducing C.

Another object of the present invention is to provide a steel sheet high in the anticorrosion against carbonated beverages by defining the S, P, and cu contents and reducing the C content.

A further object of the present invention is to cheaply provide a steel sheet high in the anticorrosion and workability by ,cold-rolling in one step.

Other objects of the present invention will be made clear from the following description and the accompanying drawings.

In order to attain the above-mentioned objects, the present invention is to obtain a steel sheet having a final thickness of less than 0.5 mm. and a hardness elevated to be higher than T-6 [of a tempered degree of 67 to 73 as a Rockwell hardness (R 30T)] by hot-rolling a steel sheet containing less than 0.030% C or preferably less than 0.018% C, 0.0200.l0% S or preferably 0.025 0.034% S, S/P being 1, less than 0.30% Si and 0.09- 1.0% Mn, the rest being substantially Fe and cold-rolling in one step this hot-rolling sheet at a reduction rate of more than Particularly, this invention is characterized by the carbon content of the steel material being very low and the carbon content being reduced by containing a proper amount of S. A steel sheet for cans of such low carbon content has never been industrially produced. Further, the process of the present invention is characterized by subjecting the steel material to a cold-rolling in one step at a high reduction rate. It can be said that such one time cold-reduction full hard material has not been used as a material for producing anticorrosive cans.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 shows relations between C contents and corrosion rate test values (blue dye values in A/cm?) with synthetic liquids presumed to be carbonated beverages; FIG. 2 shows relations between C contents in steel sheets and the life (in months) of cans containing phosphoric acid series carbonated beverage at various reduction rates in percent in cold-rolling.

DESCRIPTION OF THE PREFERRED EMBODIMENT The steel in this invention is prepared by melting in a converter or any other steel-making furnace and is ingoted, bloomed and hot-rolled by any means used today. As described above, it is necessary that the C content in the composition of the steel should be low. As a method of reducing the C content in the steel, the molten steel may be decarburized by vacuum-degassing or the hot-rolled sheet may be annealed for decarburization. Either method of reducing C has no influence on the present invention but the C content in the final product must be less than 0.03% C or preferably less than 0.018%.

There is a blue dye test as a quick testing method simulating the corrosion with carbonated beverages. In this testing method, a dye callet Blue #1 is added to about 1.2 g./l. of H PO and the reduction of weight by corrosion of a steel sheet is measured. In FIG. 1 are shown the results of measoring the C contents in percent by Weight and the blue dye values with respect to the S contents. The solid line represents the case of containing 0.02-0.03% S and the dotted line represents the case of containing no S. It is found from this graph that, when S is contained, a favorable anticorrosion is shown with the reduction of the C content and particularly, above 0.03% C, the corrosion is quickly accelerated, while, below 0.018% C the corroding rate is shown to be the lowest. On the other hand, in a steel sheet containing no S, no such remarkable anticorrosion is shown with the reduction of the C content.

In FIG. 2 are shown behaviors of C on the life of carbonated beverage cans with respect to respective coldreduction rates by varying the C content in steel sheets containing 0.10% Si, 0.45% Mn, 0.017% P and 0.035% S, the rest being substantially Fe. The life of the carbonated beverage can designates a period until a number corresponding to of the total number of cans packing phosphoric acid series or citric acid series carbonated beverages are perforated, when stored in a thermostatic temperature at 38 C.

Generally, it has been considered that, if a working strain remains, the anticorrosion will be deteriorated. But, as shown in FIG. 2, it is clear that, even if a working strain remains, the anticorrosion may be largely improved, when C is reduced to be less than 0.03%, or particularly, in the case of a high reduction of 90%, to be less than 0.018%.

That is to say, even in a steel sheet for carbonated beverage cans with the strength particularly elevated by retaining a working strain, a sufiicient anticorrosion may be obtained by limiting the range of C to be low, besides the conventional regulation of P, S and Cu.

Further, it is necessary to make the C content as low as possible to be less than 0.03% also for the purpose of increasing the can-making workability of the cold-rolled steel sheet. If a high C content is present, the carbide content in the steel becomes so high that the steel is no longer endurable to the slightest working.

In the present invention, a hot-rolled steel sheet is made a product by being cold-rolled in only one step at a high reduction rate and the strength of the steel sheet can be elevated by this high reduction cold-rolling in one step.

In this case the hardness is required to be at least T-6 to be able to bear the inner pressure of a material packed in a can. Further, in the present invention such a thin steel sheet as of less than 0.5 mm. thick, preferably 0.25 to 0.3 mm. thick, which has, however, the said thickness of at least T-6, is used as a material for a making a can. This is, however, mainly due to an economic reason. A steel sheet having the thickness of more than 0.5 mm. is practically not used on account of a rise of cost.

The reasons for defining the range of the composition of the steel sheet in the present invention shall be briefly explained in the following.

Si is an element necessary in making steel. If it is present in a large amount, the anticorrosion against carbonated beverages is reduced. Therefore, Si is defined to be less than 0.3 for a steel material for cans.

r Mn is added not only to prevent the hot-brittleness of the steel material from being caused by S, which is to be added to elevate the anticorrosion, but also to impart a required strength. Its range is 0.09 to 1.0%. Mn must be present in the steel in an amount 6 to 7 times as large as of S.

It is preferable for the improvement of the anticorrosion of the can-making material that P is contained as little as possible. But, it is diflicult in the steel-making technique to entirely eliminate P. However, in the present invention, if the amount of P is smaller than that of S, the anticorrosion can be well improved. That is, it is necessary that the P content should be smaller than the S content in the steel.

If S is less than 0.02%, no sufiicient anticorrosion against carbonated beverages can be obtained. If it is more than 0.10%, cracks are produced in hot-working.

Cu is added as required. With more than 0.1% Cu, an anticorrosion is shown against such carbonated beverages as of citric acid, tartaric acid and phosphoric acid. If it is contained in a large amount, the surface of the steel sheet becomes rough. Therefore, the upper limit of Cu is made 0.3%.

The can material of the present invention is cleaned on the surface and is tin-plated or chemically treated.

Examples of the present invention shall be described in the following but the invention is not limited to them.

The following table shows results of anticorrosion tests, wherein a slab obtained from a molten steel prepared in a converter and vacuum-degassed was hot-rolled and then cold-rolled at a high reduction rate in one step to make a steel sheet of a thickness of 0.3 mm., the steel sheet was then tin-plated.

The can was filled with a carbonated beverage and its anticorrosion was tested.

COmJOSllSlOIl of steel (percent): 0

10 0.005 0.016 0.017 0. 006 0. 006 0. 45 0. 32 0. 33 0. 3O 0. 33 0.01 0.01 0.01 O. 01 0. 01 0. 030 0 012 0.014 O. 012 0.015 0.050 0 026 0. 024 0.027 0.028 Cu 0. 06 0. 05 0. 16 0. 05 0. 18 Cold-rolling reduct 11 rate (percent) 87 87 87 87 81 81 Can lite (month):

Cola-type carbonated beverage 14 14 13 15 15 Lemon, lime-type carbon- I ated beverage 4 11 1O 16 11 17 Tensile strength (kg/111m 93 84 86 81 83 Hardness (R 30-1) 85 81 83 83 80 80 Can-producing property X 0 O O O O NOTES.-(l) The can lite designates the period until 10% ol the total cans become perforated. (2) The can was filled with a carbonated beverage. (3) The storing temperature was 38 C. (4) The can-making property was judged with beer cans. The mark 0 represents a high formabillty. The mark X represents a low iormability.

In the table, the sample No. 1 is a conventional product. Its can life is short in spite of the fact that it contains more S or S and Cu than in each of the samples Nos. 2, 3, 4, 5 and 6 which are products of the present invention.

As described above, particularly in case the strength is elevated by retaining a working strain, the can material of the present invention can exhibit an anticorrosion specially effective against a substance containing or generating carbon dioxide.

By the way, a can material not requiring such anticorrosion can be made by the above described process without containing S and Cu.

We claim:

1. A process for producing steel sheets high in the anticorrosion and particularly adapted for materials for making cans for carbonated beverages comprising subjecting a hot-rolled steel sheet containing less than 0.03 C, 0.09 to 1.0% Mn, less than 0.3% Si and 0.02 to 0.10% S, S/P being 1 and the rest being unavoidable impurities and Fe to a cold-rolling in one step at a reduction rate of more than 80% to make a product of the final thickness thereby.

2. The process for producing steel sheets according to claim 1, wherein the hot-rolled steel sheet is cold-reduced to the final thickness of less than 0.5 mm. with the hardness of at least T6.

3. A process for producing steel sheets high in the anticorrosion and particularly adapted for material for making cans for carbonated beverages, comprising subjecting a hot-rolled steel sheet containing less than 0.03% C, 0.09 to 1.0% Mn, less than 0.3% Si, 0.02 to 0.10% S and 0.1 to 0.3% Cu, S/P being 1 and the rest being unavoidable impurities and Fe to a cold-rolling in one step at a reduction rate of more than 80% to make a product of a final thickness thereby.

4. The process for producing steel sheets according to claim 3, wherein the hot-rolled steel sheet is cold-reduced to the final thickness of less than 0.5 mm. with the hardness of at least T-6.

6 References Cited UNITED STATES PATENTS 2,172,427 9/1939 Wulif 14812 5 2,589,881 3/1952 Sims et a1. 72700 3,368,886 2/1968 Muta et a1. 14812 3,382,700 5/1968 Heitmann et a1. 72700 LOWELL A. LARSON, Primary Examiner 10 US. 01. X.R. 

